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Thus, the accuracy of clocks is fundamentally limited.
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They found that an ideal clock - one that ticks with perfect periodicity - would burn an infinite amount of energy and produce infinite entropy, which isn’t possible. “A clock is a flow meter for entropy,” said Milburn. In their first paper, published in Physical Review X in 2017, Erker, Huber and co-authors showed that better timekeeping comes at a cost: The greater a clock’s accuracy, the more energy it dissipates and the more entropy it produces in the course of ticking.
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The more regular the ticks, the more accurate the clock. We reserve that name, the clock thermodynamicists realized, for objects whose timekeeping ability is enhanced by periodicity: some mechanism that spaces out the intervals between the moments when irreversible processes occur. This is why we don’t refer to coffee, or garbage or wrinkles, as clocks. This means you have to average over long stretches of time, encompassing many random collisions between coffee and air molecules, in order to accurately estimate a time interval. As with most irreversible processes, its interactions with the surrounding air happen stochastically. “This shift in perspective is what we wanted to explore.”Ĭoffee doesn’t make a great clock. “The irreversibility is really fundamental,” Huber said. Not only do energy’s strong spreading tendency and entropy’s resulting irreversible rise seem to account for time’s arrow, but according to Huber and company, it also accounts for clocks. This numerical asymmetry, and the curious fact that energy started out ultra-concentrated at the beginning of the universe, are why energy now moves toward increasingly dispersed arrangements, one cooling coffee cup at a time.
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Energy tends to dissipate - and entropy, a measure of its dissipation, tends to increase - simply because there are far, far more ways for energy to be spread out than for it to be highly concentrated. “You could tell time by measuring how cold your coffee has gotten on your coffee table,” said Huber, who is now at the Technical University of Vienna and the Institute for Quantum Optics and Quantum Information Vienna.Įarly in their conversations in Barcelona, Huber, Erker and their colleagues realized that a clock is anything that undergoes irreversible changes: changes in which energy spreads out among more particles or into a broader area. Garbage announces the days with its worsening smell. The first thing to note is that pretty much everything is a clock. Gerard Milburn, a quantum theorist at the University of Queensland in Australia who wrote a review paper last year about the research on clock thermodynamics, said, “I don’t think people appreciate just how fundamental it is.” What a Clock Is “This line of work does grapple, in a fundamental way, with the role of time in quantum theory,” Yunger Halpern said. The new perspective on clocks has already provided fresh fodder for discussions of time itself. Nicole Yunger Halpern, a quantum thermodynamicist at Harvard University who was not involved in the recent clock work, called it “foundational.” She thinks the findings could lead to the design of optimally efficient, autonomous quantum clocks for controlling operations in future quantum computers and nanorobots. These relationships were purely theoretical until this spring, when the experimental physicist Natalia Ares and her team at the University of Oxford reported measurements of a nanoscale clock that strongly support the new thermodynamic theory. They realized that these theoretical frameworks, which undergird emerging technologies like quantum computers and quantum engines, also provided the right language for describing clocks. Huber, Erker and their colleagues specialized in quantum information theory and quantum thermodynamics, disciplines concerning the flow of information and energy. There, a whole cadre of physicists took up Erker’s question, led by a professor named Marcus Huber. Then in 2015, he moved to Barcelona for his doctorate. The budding physicist started thinking for himself about what a clock is - what it takes to tell time. “I was very unsatisfied by the way the literature so far dealt with clocks,” Erker said recently. They tended to take time information for granted. “Time is what a clock measures,” Albert Einstein famously quipped Erker hoped a deeper understanding of clocks might inspire new insights about the nature of time.īut he found that physicists hadn’t bothered much about the fundamentals of timekeeping. In 2013, a masters student in physics named Paul Erker went combing through textbooks and papers looking for an explanation of what a clock is.